[Update]: CD Projekt Red will be drastically slowing down development on Gwent: The Witcher Card Game in 2023 and beyond.
Following in the footsteps of Thronebreaker: The Witcher Tales, the standalone version of The Witcher 3's Gwent has now launched another singleplayer-focused expansion. However, instead of being a story-based adventure with the occasional Gwent game to spice things up, the newly released Rogue Mage is more of a roguelike and deckbuilding strategy game similar to Slay the Spire.
What this looks like in actual gameplay, as well as what the story is even about, that you can get a bit of a sneak peek at through the trailer below. Have a gander:
As for whether it's any good or not, that's a tricky question to answer. Rogue Mage is by no means terrible, especially not given the $10 price tag, but it's also not exactly exciting since it lacks some of the intricacies of Gwent itself. Replay value is also highly limited since there isn't as much diversity as in something like Slay the Spire, which just leaves Rogue Mage in a kind of an awkward spot.
So unless you're a big fan of Gwent, I'd recommend either skipping Rogue Mage or grabbing it at a discount later down the line. It's a solid attempt at a roguelike, and something I'd like to see CDPR iterate on with future expansions and updates, but right now it's just a bit too basic to recommend over the much more fleshed out competitors.
Whatever your thoughts on the matter may be, you can learn more about Gwent: Rogue Mage, as well as check out some of the player reviews, over at Steam. Enjoy!